1. Field of the Invention
The present invention relates to a radome for protecting a radio wave device from the outside environment, and a method of producing the same. More particularly, the present invention relates to a radome for use in aircraft, vehicles, etc., and a method of producing the same.
2. Description of the Related Art
Radomes must not block the radio waves to be received, transmitted, or received/transmitted by a radio wave device and must have the structural strength required to protect the radio wave device from the outside environment. Mentioned as a conventional radome having such properties there are radomes using a composite material having reinforced fiber in a matrix resin, i.e., a single layer panel formed of a fiber reinforced plastic. Moreover, there are also radomes using sandwich structure panels in which a core formed of a low density dielectric such as a foamed body is sandwiched between a first composite material facing having a reinforced fiber in a matrix resin and a second composite material facing opposite to the first composite material facing (e.g., see JP 2007-519298 T). Such sandwich structure panels can reduce the dielectric constant as a whole while maintaining the structural strength by sandwiching a low density dielectric therein. Therefore, the sandwich structure panels can improve the transmission loss of radio waves to thereby improve the properties of a radome as compared with a single layer panel formed of a fiber reinforced plastic.
Here, as the reinforced fiber, a glass fiber is generally used. From the viewpoint of further reducing the dielectric constant, it is also known to use a fiber such as polyester-polyarylate fibers and ultrahigh molecular weight olefin fibers in which the dielectric constant of the fiber itself is low (e.g., JP 2007-519298 T and JP 06-10233 A).
However, in the case of using a fiber reinforced plastic in which a glass fiber is used as a reinforced fiber, a large amount of glass fiber needs to be added to a matrix resin so as to achieve the rigidity required in a radome. Since the dielectric constant of generally-used glass is about 4 to about 7 (e.g., the dielectric constant of E-Glass which is a glass fiber generally used for electrical applications is 6.6), such a fiber reinforced plastic cannot reduce the dielectric constant. Thus, a radome using such a material has increased transmission loss of radio waves.
In contrast, in the case of using, as a reinforced fiber, an organic fiber having a low dielectric constant such as polyester-polyarylate fibers and ultrahigh molecular weight olefins, the dielectric constant can be reduced. However, since organic fibers having a low dielectric constant generally have a weak adhesion force with a matrix resin, the interface between the organic fiber and the matrix becomes slippery. As a result, a radome using such a material is likely to suffer from plastic deformation when distortion in the bending direction is applied by a load such as wind.
Moreover, by the use of a glass cloth as a reinforced fiber for the composite material facing of the sandwich structure panels of JP 2007-519298 A, plastic deformation can be prevented. However, since the dielectric constant of the core is considerably different from the dielectric constant of the composite material facing, reflection is likely to occur when a radio wave transmits between the composite material facing and the core and, moreover, the number of side lobes increases remarkably, resulting in increased transmission loss of radio waves.
Further, a method of producing a radome using sandwich structure panels has problems with workability. More specifically, although it is possible to form a radome having a curved surface shape, it is difficult to form a radome having an angled portion. Specifically, when the core material of the sandwich structure panels is folded or two or more of the core materials are connected in producing the sandwich structure panels, the density becomes coarse due to the formation of cracks and compression parts in the core material, which become a singular point of the dielectric constant, resulting in increased transmission loss of radio waves. Moreover, in the method of producing a radome using sandwich structure panels, the first composite material facing, the second composite material facing, and the core are produced separately, and then the composite material facings and the core need to be laminated with each other, giving rise to problem that the production process is complicated.
The present invention has been made in order to solve the above-mentioned problems. An object of the present invention is to provide a radome which has excellent transmission loss of radio waves and structural strength, which can be easily produced, and which has favorable workability, and a method of producing the same.